The present invention relates generally to blocking audio-video television signals and specifically to retrofitting audio-video signal receivers with a signal blocking device so that users can prevent reception of programming having a rating signal greater than that selected by the user.
Television is an important medium of information and entertainment in modern society. To encompass the differing tastes and standards of individual viewers, networks and local TV stations broadcast violent and adult theme programs as well as other types of programming that viewers might find objectionable or inappropriate for children. Parents may not want their children to view these programs, but they cannot always monitor their children's viewing habits. Other viewers, too, may not wish to receive what they consider to be objectionable programming.
The patent literature describes systems that can block or prevent objectionable programs. For example, U.S. Pat. No. 4,554,584 issued to Elam et al. discloses a video and audio blanking system with an auxiliary circuit that detects and decodes digital code words transmitted as part of the video signal. The disclosed system will blank the audio or video portion, or both, of the transmitted signal according to the transmitted code. The system disclosed in Elam et al., as well as those disclosed generally in the prior art shows the video and audio blanking circuitry in the television tuner.
Another example of this is U.S. Pat. No. 4,225,884 issued to Block et al. which discloses subscriber station equipment that may include program access and control including a category selection knob allowing the subscriber to operate a key-controlled switch that can be locked and tuned to a particular category of programming. The category knob includes a pointer indicator that can be turned to a number of different category positions. The categories can represent classifications of broadcast programs based on the subject matter content of the programs. Block et al. discloses a category selection feature to permit selective control by the subscriber of the programs that can be viewed. Block et al. also discloses that the key lock selector knob allows parents to prevent unauthorized viewing by children of programs having sensitive subject matter. The circuitry, however, is internal to the television.
One problem with existing signal blocking devices is that they are designed to be installed as part of the customer equipment, such as the TV or cable box. Not all TVs or cable boxes have such circuitry, however. Moreover, merely adding a signal blocking circuit in series with the TV is unsatisfactory. Someone can disconnect the circuit and render it useless.
A need therefore exists to retrofit TVs and other audio/video equipment with tamper-resistant signal blocking technology. Such a retrofit device should block signals having a certain rating code, the signals being broadcast, cable, satellite (so-called direct broadcast satellites), VCR, or any other type of signal received by a TV. To prevent tampering, the a retrofit device should also block signals if the connections between the retrofit signal blocking device and the TV are not properly made. It would also be desirable if the retrofit device gave an audible or visual warning when objectionable material is being broadcast.